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    Discussion in 'Calculations' started by LandroverDom, Sep 28, 2010.

    1. LandroverDom

      LandroverDom Member

      Sep 2010
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      I am currently involved in a project for the construction of a new pressure vessel. The design is being fully checked by persons accredited to check againt the applicable design code to ensure 100% safety and complience so no concerns on that point.

      This vessel is fairly large and the pressures / forces are significant.

      Someone in the office asked a questien "if the cap blew off how high vertically could it reach?". Whilst every effort is being put in place to ensure this can never happen it made me realise that I am a bit sketchy on how to go about making the calculation and I am also interested in what the answer would be.

      I think the criteria that would be needed for the calculation is as follows.

      Weight of cap assembly = 950kg
      Pressure inside vessel during Hydro Test = 33,031psi
      Bore diameter = 400mm
      Area on cap pressure is acting against = 128825mm^2
      Medium inside vessel = Hydraulic Oil
      Calculated oil compression inside vessel = 18 liters

      So at test pressure the force trying to blow the cap off I get to be 28,082Kn (just less than 2900 tons!)....pretty huge!

      This cap will not fail but theoretically if it did I would be interested in how to calculate the initial MPH of the cap travelling vertically upwards (the vessel is mounted in the vertical) and what would be the maximum height achieved and I guess how long would it take to achieve maximum height.

      I expect the answers will be farly shocking?? I would like to know how to calculate the answers from an interest point of view but also to advise operators of whats involved with this vessels and to stress the importance of following procedures and to never cut corners etc etc.

      Many Thanks

    3. mvalenti

      mvalenti Well-Known Member

      Nov 2009
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    4. cwarner7_11

      cwarner7_11 Well-Known Member

      Oct 2009
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      Back in the 1980's I was employed at Southwest Research Institute in San Antonio, Texas, where we had a number of high pressure test vessels, some of them installed vertically. One of the vessels I worked with was capable of 10,000 psi and had an internal diameter of something on the order of 2 meters. While I have had fittings fail ( a really spectacular event in itself!), I have never seen one of the lids launched, although local legend was that it had happened once in the past, and the lid supposedly achieved an elevation on the order of 1200 feet, fortunately, returning to ground in an open field). I do know that we had to notify the local airport authorities when we were conducting tests in these vessels. Back in the days, I did the calculations because the 1200 feet sounded outrageous to me, and found that it was reasonable, in spite of the weight of the lid. The formula involved pressure times area, an estimation of wind resistance, and some very, very accurate numbers for gravity (not because they were necessary, but because they were available at the Institute). I believe the greatest unknown was the actual weight of the lid- had to estimate it based on geometry and material density. I don't remember the calculations exactly, but it was pretty much standard ballistics.

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